This invention relates to electronic systems, and is concerned with a system comprising a manipulable electronic light sensor, commonly known as a light pen, which is mounted so that it can selectively be placed in front of an electronic light emitting device for control or information transmission purposes.
It has been proposed to use a light pen to detect the time of arrival of the scanning spot at a particular part of a cathode ray tube (CRT) acting as a television screen or visual display unit (VDU), see for example U.S. Pat. Nos. 3,181,154; 3,492,657 and 4,017,680. In response to this, the operation of data processing circuits can be controlled. In these prior proposals a time/position or coordinate detection system is used to establish the position of the light pen on the CRT, by detecting the instant at which the scanning spot is sensed by the light pen.